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Raw Input and Output in Java
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Background
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  • The Foundation:
    • Most text I/O in Java is stream oriented
  • An Important Design Pattern:
    • Raw I/O in Java makes heavy use of the decorator pattern (however, since there is no interface at the top, each decorator both extends its parent and delegates important operations to its parent)
Raw I/O Fundamentals
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  • Purpose:
    • Provide the ability to read and write bytes
  • History:
    • Was originally the only way to do I/O in Java until support for character encodings was added
Important Examples
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  • Standard Error/Output:
    • System.out is a PrintStream java.io.PrintStream object
    • System.err is a PrintStream java.io.PrintStream object
  • Standard Input:
    • System.in is a InputStream java.io.InputStream object
Some Streams for Input
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images/streams_input.gif
Some Streams for Output
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images/streams_output.gif
The OutputStream Class
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  • The write() Methods:
    • Write a byte or array of bytes
  • Other Methods:
    • close()
    • flush()
  • Assessment:
    • Is not "friendly" but can be decorated to add functionality
The PrintStream Class
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  • The print() and println() Methods:
    • Versions for all standard types (overloaded)
    • Unformatted
    • Print a single value
  • The printf() Method:
    • A convenient way to use format strings (which are encapsulated in Formatter java.util.Formatter ) to format and print multiple values at the same time
The InputStream Class
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  • The read Methods:
    • Read a byte or array of bytes
    • Is not "friendly"
  • Other Methods:
    • available()
    • skip()
  • Assessment:
    • Is not "friendly" but can be decorated to add functionality
The DataInputStream Class
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  • The readLine() Method:
    • Reads a complete line, returning a String
    • Has been deprecated because of conversion problems
  • Other Methods:
    • Can be used to read primitive data types
Reading Until End-of-Stream
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javaexamples/streams/Googler.java
 
Motivating Piped Streams
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A Driver for the Googler

javaexamples/streams/GooglerDriver1.java
 
Motivating Piped Streams (cont.)
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  • A Problem with the Driver:
    • You can't prompt the user for each line of input
  • A Solution:
    • Use piped streams
  • A Warning:
    • The source and sink should be accessed from different threads
A Factory for Piped Streams
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javaexamples/streams/PipedStreamFactory.java
 
Using Piped Streams
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A Better Driver for the Googler

javaexamples/streams/GooglerDriver2.java
 
Using a Byte Array Stream
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Putting a String in a Stream
javaexamples/streams/StreamFactory.java (Fragment: String)
 
There's Always More to Learn
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